Showing papers by "Imperial College London published in 1993"

Novel approach to nonlinear/non-Gaussian Bayesian state estimation

Abstract: An algorithm, the bootstrap filter, is proposed for implementing recursive Bayesian filters. The required density of the state vector is represented as a set of random samples, which are updated and propagated by the algorithm. The method is not restricted by assumptions of linear- ity or Gaussian noise: it may be applied to any state transition or measurement model. A simula- tion example of the bearings only tracking problem is presented. This simulation includes schemes for improving the efficiency of the basic algorithm. For this example, the performance of the bootstrap filter is greatly superior to the standard extended Kalman filter.

The Kondo Problem to Heavy Fermions

Abstract: 1. Models of magnetic impurities 2. Resistivity calculations and the resistance minimum 3. The Kondo problem 4. Renormalization group calculations 5. Fermi liquid theories 6. Exact solutions and the Bethe ansatz 7. N-fold degenerate models I 8. N-fold degenerate models II 9. Theory and experiment 10. Strongly correlated fermions Appendices.

Spectral Analysis for Physical Applications

Abstract: Note: Includes bibliographical references and indexes Reference Record created on 2004-09-07, modified on 2016-08-08

Amyotrophic lateral sclerosis and structural defects in Cu,Zn superoxide dismutase

Abstract: Single-site mutants in the Cu,Zn superoxide dismutase (SOD) gene (SOD1) occur in patients with the fatal neurodegenerative disorder familial amyotrophic lateral sclerosis (FALS). Complete screening of the SOD1 coding region revealed that the mutation Ala4 to Val in exon 1 was the most frequent one; mutations were identified in exons 2, 4, and 5 but not in the active site region formed by exon 3. The 2.4 A crystal structure of human SOD, along with two other SOD structures, established that all 12 observed FALS mutant sites alter conserved interactions critical to the beta-barrel fold and dimer contact, rather than catalysis. Red cells from heterozygotes had less than 50 percent normal SOD activity, consistent with a structurally defective SOD dimer. Thus, defective SOD is linked to motor neuron death and carries implications for understanding and possible treatment of FALS.

Bayesian Computation Via the Gibbs Sampler and Related Markov Chain Monte Carlo Methods

Abstract: The use of the Gibbs sampler for Bayesian computation is reviewed and illustrated in the context of some canonical examples Other Markov chain Monte Carlo simulation methods are also briefly described, and comments are made on the advantages of sample-based approaches for Bayesian inference summaries

Rare species, the coincidence of diversity hotspots and conservation strategies

Abstract: SPECIES conservation in situ requires networks of protected areas selected for high conservation interest1–3. Throughout most of the world, however, there are neither the resources nor the time to carry out detailed inventories for most taxa2,4 before designating protected areas. Site selection (on grounds other than availability) would be easier and more effective if two things were true: (1) habitats that are species-rich for one taxon are also species-rich for others5; and (2) rare1 species occur in, and therefore benefit from the conservation of, species-rich habitats. Diversity (usually, species richness) and the presence of rare species are the most frequently cited criteria for site selection by conservationists6–8. Here, we use data on British plants and animals held by the Biological Records Centre (BRC)9 and the British Trust for Ornithology (BTO), mapped on a grid of 10 km × 10 km ('10 km squares') to examine the extent to which species-rich areas for different taxa coincide, and whether species-rich areas contain substantial numbers of rare species. The fine scale and high intensity of recording in Britain produces distributional datasets at least as good as and, in most cases, better than those available elsewhere. For Britain at least, we do not find strong support for either proposition. Species-rich areas ('hotspots'10) frequently do not coincide for different taxa, and many rare species do not occur in the most species-rich squares.

The Jaynes-Cummings Model

Abstract: The Jaynes-Cummings model (JCM), a soluble fully quantum mechanical model of an atom in a field, was first used (in 1963) to examine the classical aspects of spontaneous emission and to reveal the existence of Rabi oscillations in atomic excitation probabilities for fields with sharply defined energy (or photon number). For fields having a statistical distributions of photon numbers the oscillations collapse to an expected steady value. In 1980 it was discovered that with appropriate initial conditions (e.g. a near-classical field), the Rabi oscillations would eventually revive, only to collapse and revive repeatedly in a complicated pattern. The existence of these revivals, present in the analytic solutions of the JCM, provided direct evidence for discreteness of field excitation (photons) and hence for the truly quantum nature of radiation. Subsequent study revealed further non-classical properties of the JCM field, such as a tendency of the photons to antibunch. Within the last two years it ha...

Handbook of logic in artificial intelligence and logic programming (vol. 1)

Abstract: Introducing a new hobby for other people may inspire them to join with you. Reading, as one of mutual hobby, is considered as the very easy hobby to do. But, many people are not interested in this hobby. Why? Boring is the reason of why. However, this feel actually can deal with the book and time of you reading. Yeah, one that we will refer to break the boredom in reading is choosing handbook of logic in artificial intelligence and logic programming vol 3 nonmonotonic reasoning a as the reading material.

Individual patterns of functional reorganization in the human cerebral cortex after capsular infarction.

Abstract: We have previously shown bilateral activation of motor pathways and the recruitment of additional motor areas in studies of groups of patients with recovery from motor stroke. We have now developed a new positron emission tomographic technique to measure the changes in regional cerebral blood flow elicited during a motor task in individual patients, relative to the cerebral activation found in normal subjects. The patterns of cerebral activation in each of 8 individual patients with capsular lesions of the pyramidal tract and complete recovery from hemiplegia are described by comparison with the pattern found in a representative sample of 10 normal subjects. We found a large ventral extension of the hand field of the contralateral (sensori)motor cortex in all patients with lesions of the posterior limb of the internal capsule. Greater activation than in normal subjects was found in variable combinations of the supplementary motor areas, the insula, the frontal operculum, and the parietal cortex. Structures belonging to motor pathways ipsilateral to the recovered limb were also more activated in the patients than in normal subjects. However, additional activation of the ipsilateral (sensori)motor cortex was only found in the 4 patients who exhibited associated movements of the unaffected hand when the recovered hand performed the motor task. We conclude that recovery from motor stroke due to striatocapsular damage is associated with individually different patterns of functional reorganization of the brain. These patterns are dependent on the site of the subcortical lesion and the somatotopic organization of the pyramidal tract, both of which may determine the precise potential for recovery of limb function following this type of brain injury.

Range, population abundance and conservation

Abstract: Several patterns in the distribution and abundance of organisms have now been documented. They include broad (but not universal) positive correlations between range sizes and population abundances; a decline in the proportion of sites occupied and in average population densities from the centre to the edge of a species' range, with either unimodal or multimodal peaks of abundance and occupancy in the core of the range; and intriguing, but still poorly documented phylogenetic effects on both range size and abundance. All these patterns require further work to establish their generality, and all of them lack generally agreed explanations. They are important, however, not only theoretically but also practically, because of the constraints and opportunities they appear to provide for the management and conservation of species.

Modelling of Railway Track and Vehicle/Track Interaction at High Frequencies

Abstract: A review is presented of dynamic modelling of railway track and of the interaction of vehicle and track at frequencies which are sufficiently high for the track's dynamic behaviour to be significant. Since noise is one of the most important consequences of wheel/rail interaction at high frequencies, the maximum frequency of interest is about 5kHz: the limit of human hearing. The topic is reviewed both historically and in particular with reference to the application of modelling to the solution of practical problems. Good models of the rail, the sleeper and the wheelset are now available for the whole frequency range of interest. However, it is at present impossible to predict either the dynamic behaviour of the railpad and ballast or their long term behaviour. This is regarded as the most promising area for future research.

Immunological modulation and evasion by helminth parasites in human populations

Abstract: Helminth parasites are highly prevalent in human communities in developing countries. In an endemic area an infected individual may harbour parasitic worms for most of his or her life, and the ability of these infections to survive immunological attack has long been a puzzle. But new techniques are starting to expose the diverse mechanisms by which these agents modulate or evade their hosts' defences, creating a dynamic interaction between the human immune system and the parasite population.

European option pricing with transaction costs

Abstract: The authors consider the problem of pricing European options in a market model similar to the Black–Scholes one, except that proportional transaction charges are levied on all sales and purchases o...

The ecology of insect overwintering

Abstract: Foreword 1. Introduction 2. The overwintering locale - suitability and selection 3. The stimuli controlling diapause and overwintering 4. Insect cold-hardiness 5. Costs and benefits of overwintering 6. Prediction and control Bibliography Index.

Robotic surgery

Abstract: The application of an active surgical robot, the Surgical Assistant Robot for Prostatectomy (SARP), to transurethral resection of the prostate is discussed. SARP performs surgery under the supervision of a surgeon. The mechanical construction computing system, software, motion controller and image system of SARP are discussed. >

Non–invasive liposome–mediated gene delivery can correct the ion transport defect in cystic fibrosis mutant mice

Abstract: We report gene transfer to the Edinburgh insertional mutant mouse (cf/cf), delivering CFTR cDNA-liposome complexes into the airways by nebulization. We show full restoration of cAMP related chloride responses in some animals and demonstrate, in the same tissues, human CFTR cDNA expression. Overall, a range of correction was seen with restoration of about 50% of the deficit between wild type mice and untreated cf/cf controls. We report modest correction in the intestinal tract following direct instillation and provide initial encouraging safety data for both the respiratory and intestinal tract following the liposome mediated gene delivery. The non-viral nature and potentially lower immunogenicity of DNA-liposomes suggest that this may offer a therapeutic alternative to adenoviral therapies.

The influence of age on the development of the hepatitis B carrier state

Abstract: The relation between the age at infection with hepatitis B virus (HBV) and the development of the carrier state is examined by using data from a number of published and unpublished surveys. A remarkably consistent relation was found. Infants infected perinatally (within the first 6 months of life) were found to have a high probability of becoming carriers (0.885; 95% C.L. 0.84-0.93). Over the infant and early childhood age classes there was found to be a sharp decrease in the proportion of infections which lead to the carrier state. By adulthood (over 15 years) the probability of developing the carrier status was found to be about 0.1. A model was fitted to the data by using maximum likelihood, which provides a good empirical description of the observed data and can be used to predict the expected probability of developing the carrier state given the age at infection. It is postulated that, as a result of this rapid decline in the probability of becoming a carrier during early childhood, a mass childhood immunization campaign, which will tend to postpone the average age at infection in the unvaccinated community, will have a disproportionately large impact on the rate of generation of new carriers.

The interaction of Lamb waves with delaminations in composite laminates

Abstract: The S0 Lamb mode can propagate over distances of the order of 1 m in composite laminates and so has the potential to be used in long‐range nondestructive inspection. This paper discusses the interaction of the S0 Lamb mode with delaminations. The dispersion curves and the corresponding stress and displacement mode shapes of the lower order Lamb modes are obtained analytically and the interaction of the S0 mode with delaminations at different interfaces in a composite laminate is then studied both by finite element analysis and by experiment. It is shown that the amplitude of the reflection of the S0 mode from a delamination is strongly dependent on the position of the delamination through the thickness of the laminate and that the delamination locations corresponding to the maximum and minimum reflectivity correspond to the locations of maximum and minimum shear stress across the interface in the S0 mode.

Latitudinal patterns in European ant assemblages: variation in species richness and body size

Abstract: Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.

Parallel Programming Using Skeleton Functions

Abstract: Programming parallel machines is notoriously difficult. Factors contributing to this difficulty include the complexity of concurrency, the effect of resource allocation on performance and the current diversity of parallel machine models. The net result is that effective portability, which depends crucially on the predictability of performance, has been lost. Functional programming languages have been put forward as solutions to these problems, because of the availability of implicit parallelism. However, performance will be generally poor unless the issue of resource allocation is addressed explicitly, diminishing the advantage of using a functional language in the first place.

Management guidelines in essential hypertension: report of the second working party of the British Hypertension Society.

Abstract: Several important new issues have arisen in the management of patients with hypertension. A working party of the British Hypertension Society has therefore reviewed available intervention studies on anti-hypertensive treatment and made recommendations on blood pressure thresholds for intervention, on non-pharmacological and pharmacological treatments, and on treatment goals. This report also provides guidelines on blood pressure measurement, essential investigations, referrals for specialist advice, follow up, and stopping treatment.

An E2F-binding site mediates cell-cycle regulated repression of mouse B-myb transcription.

Abstract: Transcription of the B-myb gene is regulated at the G1/S boundary of the cell cycle. To begin to examine the mechanism controlling expression of this gene during the cell-cycle, a mouse B-myb 5' flanking sequence was isolated from a cosmid library and shown to promote efficiently the transcription of a luciferase reporter gene when transfected into NIH3T3 fibroblasts. It was further shown that in transfected cells released from G0 by readdition of serum, luciferase activity directed by the B-myb promoter was induced substantially as cells entered S phase, thus paralleling the regulation of endogenous B-myb. Analysis of the B-myb promoter identified a region that appeared to have no intrinsic promoter activity yet which acted to regulate transcription negatively in G0. Mutagenesis of an E2F consensus binding site within this region was sufficient to relieve transcription repression in G0, resulting in a promoter with constitutively high activity. Specific G0 and S phase E2F complexes binding to this B-myb element were detected in NIH3T3 cell extracts by mobility shift assays. These studies demonstrate for the first time a direct role for E2F in regulation of cell cycle gene expression by repression of transcription in G0/early G1.